By Warren Tenney
For many years, the State of Arizona has been storing water underground to prepare for times of drought. One way Arizona has accomplished this is through the efforts of a little-known state agency called the Arizona Water Banking Authority, commonly known as the Water Bank. Since its establishment in 1996, the Water Bank has stored Arizona’s unused Colorado River water underground, rather like a savings account. This savings account acts as a buffer if shortages cut water supplies from the Central Arizona Project (CAP). The CAP is a 336-mile canal that transports Colorado River water across the state to central Arizona and the Valley. If necessary, the Water Bank will use this stored water to replace certain water supplies needed by cities, industrial users, and tribes when drought and shortage hits the Colorado River.
The creation and operation of the Water Bank is one of Arizona’s water success stories. Arizona has done an excellent job storing water underground. Since its establishment 20 years ago, the Water Bank has stored 3.4 million acre-feet of CAP water. One acre-foot is enough water to supply 3 average Arizona households for one year. This water is in addition to the water Arizona cities have stored underground for decades within city limits or in regional underground storage facilities.
The next challenge is to complete the plan for the eventual pumping or “recovery” of the Water Bank’s water. How this water is recovered is one of the most important issues facing municipal water providers in the Phoenix area.
It is important to know that the Water Bank’s primary responsibility to date has been to store water. The agency is not equipped to transport, recover or distribute water. Arizona law states the Water Bank and CAP are to work together on recovering stored water. CAP has significant infrastructure in place and the ability to develop more, so CAP’s involvement is critical to ensure the eventual recovery of this water.
Understanding the importance of defining how recovery would occur, the Arizona Department of Water Resources (ADWR), CAP, and the Water Bank in 2014 jointly developed basic principles about how to recover stored water during a shortage. While the respective agencies have made progress in planning for recovery, additional work is needed so municipalities have greater certainty as to how recovery of this stored water will occur and meet their needs.
AMWUA recently identified and analyzed the outstanding issues that need to be resolved to provide a complete recovery plan and give the cities greater certainty. Here is a brief summary:
- Distribution of Water Credits: Every acre-foot of water stored by the Water Bank creates a credit so the Arizona Department of Water Resources can track the amount of water stored. It is not clear how these credits would be distributed during a shortage and in what amounts.
- Roles of CAP and the Water Bank: Arizona laws state that the Water Bank and CAP are to work together on recovering saved water, but it doesn’t provide specifics on their individual roles. Over the past several years, the Water Bank and CAP have worked on an agreement to clarify their roles, but that agreement is not yet final.
- Infrastructure and Costs: Pumping and delivering the water would require expensive infrastructure, such as wells, treatment facilities, and possibly the use of canals. Existing infrastructure could be used, but many water experts anticipate that additional infrastructure would be necessary.
- Water Quality: There are some unknowns about the quality of recovered water based on where the Water Bank has stored it. Testing and possible treatment of water may be required.
- Water Exchanges: Another question is whether cities and the Water Bank could engage in exchanges of water that would decrease the costs of recovering water. For example, some experts have suggested that the Water Bank could store water underground in Tucson now for the City to use during shortages. When shortages come, Valley cities could then receive Tucson’s allocation of CAP water at their existing canal-side water treatment plants. This is similar to the current agreement Phoenix has with Tucson and Metro Water District.
This is a simplified summary of a complex issue. The importance of this issue, however, is clear: While the first shortage cut won’t affect the cities, cities still want to be as well prepared as possible with their water supplies for when a shortage may impact them. The Water Bank and CAP working to clarify outstanding questions regarding recovery of stored water will give municipalities greater certainty. This is one more way in which Arizona continues to plan and be ready for whatever water challenge it must face.
For 47 years, Arizona Municipal Water Users Association has worked to protect our member cities’ ability to provide assured, safe and sustainable water supplies to their communities. For more water information visit www.amwua.org.